Descriptions

This project was initiated to determine the incidence, distribution
and species of fish affected by Ceratomyxa shasta in Oregon
waters. Returning adult Pacific salmon and steelhead trout were
chosen for the survey because they were known to be susceptible to
infection. The parasite was also believed to be an important cause
of prespawning losses.
All coho salmon samples obtained from the Columbia River
basin contained individuals infected with Ceratomyxa shasta. The
infection was greatest at the Bonneville and Sandy hatcheries, where
approximately 75 percent of the fish examined were infected. The
only coastal sample found to contain coho salmon infected with Ceratomyxa
shasta was taken from the Nehalem River. Fish that reached
the hatchery but died before the start of spawning operations were
obtained from the Klaskanine and Sandy hatcheries. The incidence of Certaomyxa shasta infected fish in these samples was in both
cases greater than in samples obtained during spawning.
Spring chinook obtained from coastal river locations (Trask and
Rock Creek hatcheries) were not infected with this parasite. Infected
spring chinook were found in all Willamette River tributaries
surveyed. The incidence was greatest (28 percent at Dexter Dam)
in fish which had migrated the farthest distance up the river.
Ceratomyxa shasta in dead fish obtained from the Dexter Dam holding
pond was over twice that found in spawned fish from this location.
The incidence and distribution of Ceratomyxa shasta in fall
chinook salmon was different from that found in coho or spring
chinook. The coastal sample obtained from the Trask Hatchery contained
one infected individual. The Klaskanine River was the only
tributary on the lower Columbia that contained infected fall chinook,
eight percent of these fish were infected. The infection was much
greater in fall chinook sampled at the Oxbow Hatchery (Snake River)
than in fish obtained from sites on the lower Columbia River. Sixty-five percent (65%) of the fish from this hatchery were infected. The
incidence of Ceratomyxa shasta in prespawning mortalities at the
Oxbow Hatchery (Snake River) was identical to that found in adults
killed at spawning.
Samples of steelhead trout obtained from the Big Creek
Hatchery and Pelton Dam contained fish infected with this disease. The number of spores per smear of infected steelhead tissue was
low when compared to the number observed in smears from coho
and spring chinook. No steelhead mortalities were obtained.
The incidence of Ceratomyxa shasta in adult salmonids does
not appear to be related to the sex of the animals. The disease incidence
appears to be related to the distance and rate of migration.
Infections in adult salmonids caused by Ceratomyxa shasta
probably occur during the freshwater phase of their life cycle.
Geographically, Ceratomyxa shasta is widely distributed
throughout the survey area. The parasite was found in all areas of
the Columbia River basin sampled. Coastal river systems found to
contain infected fish were the Nehalem and possibly the Trask. The
incidence of Ceratomyxa shasta in coastal rivers decreased progressively
from the Columbia River southward.